"where does one get Benzalkonium Chloride in a bottle?"

The active ingredient in 'non-staining' Mercurochrome, same bottle and applicator but different label, is benzalkonium chloride. In the drug store the non-staining stuff you want is sold in the next slot over from the regular stuff.

Up side to this stuff is it doesn't contain the questionable chemicals the original version does and it doesn't contain the alcohol, which was the reason nasty red stuff burned like fire.